1. Field of the Invention
This invention relates generally to sabot strippers and more specifically to a gas-dynamic, non-rotational sabot stripper.
2. Description of the Prior Art
Current techniques to separate sabot components from the flight vehicle consist of mechanical stripping, muzzle jet gas-dynamic discard, freeflight gas-dynamic discard and spin discard. These techniques are illustrated schematically in FIGS. 1-4, respectively.
A mechanical stripper 10, as illustrated in FIGS. 1 and 1A has been used in the launch of a sabot encapsulated flechette round 12 from a small caliber (5.56 mm) rifle. The stripper is a subcaliber set of keys or blades 14 located in the gun tube near the muzzle. The keys fracture the plastic or fiberglass sabot and may impart spin or lateral motion to the sabot components. The major difficulty with this technique is the adverse loadings imparted to the flight vehicle. These loadings can effect subsequent projectile motion and, through this, weapon accuracy and dispersion. Additionally, direct contact between the flight vehicle and the stripper keys can cause severe damage to the projectile integrity.
The next two techniques, as illustrated in FIGS. 2 and 3, are similar in that gas-dynamic loadings are used to bring about sabot separation and discard. They differ in the source of these loadings. One technique uses expanding propellant gas energy, while the other uses free air loads on the moving sabot components. Muzzle jet gas-dynamic discard uses the loads applied to the rear surfaces 16 of the sabot components 18 by the propellant gas to cause lateral acceleration of the components as illustrated in FIG. 2. At this point, it should be noted that when the propellant gases are permitted to expand freely from the muzzle of the gun, the gas energy is deposited over a wide area which increases geometrically with separation from the muzzle, as illustrated in FIGS. 2-4 by the arrows and dotted line. Thus, in current bare muzzle applications, propellant gas loadings decrease extremely rapidly such that, within four to five calibers of projectile travel, they are negligible. This limits the use of this source of discard energy to the separation of lightweight, e.g. plastic or rubber, sabot materiel.
Free flight gas-dynamic discard is widely used with fin stabilized projectiles. The technique, as illustrated in FIG. 3, makes use of aerodynamic loadings on the forward surfaces 20 of sabot components 22 to bring about lateral motion.
The final separation technique considered is spin or centrifugal discard. This technique, shown in FIG. 4, is applied to the discard of sabots from spin stabilized projectiles. Upon release from the muzzle of the gun, centrifugal forces destroy the structural integrity of the sabot 24 and cause the components to move away from the flight vehicle.
In general, all of the techniques mentioned rely upon aerodynamic drag to cause the sabot components to drop behind the flight vehicle as they move downrange. However, if sufficient lateral separation of sabot components may be generated near the muzzle of the gun, it would be possible to interdict sabot components through the use of deflectors or baffle plates. U.S. Pat. No. 3,533,325 is an example of use of a conical deflector to shred the sabot components, which were stripped using a combined mechanical and centrifugal force stripper.
The stripper of the present invention controls propellant gas expansion such that gas energy is concentrated in the vicinity of the projectile. This energy is then used to perform useful work in separating the sabot components from the flight vehicle. The advantage of this technique over mechanical stripping is the elimination of direct mechanical impingement between the stripper and the projectile. When compared to the bare muzzle jet gas-dynamic discard technique of FIG. 2, the current concept increases both the magnitude and duration of propellant gas loadings upon sabot components. The magnitude of loading is controlled by the channel expansion ratio, and the duration of loading is controlled by the length of the channel.
The gas-dynamic stripper technique will permit increased separation of dense sabot materials, e.g., aluminum and steel, and total discard of lighter materials, e.g., plastic and rubber. The increased rate of discard provides for a decreased time of residency of sabot components within the vicinity of the flight vehicle. This in turn decreases the interactions between sabot components and the flight vehicle. Obviously, this effect is advantageous in comparison to the longer residencies encountered with free flight gas-dynamic discard of FIG. 3. Comparison of the proposed technique with spin discard of FIG. 4 shows that similar discard properties may be achieved; however, since fin stabilized rounds are generally not spun at launch or only slowly spun, the use of gas-dynamic sabot stripping is uniquely suited to these rounds.